<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>Assert | Node.js v12.16.1 Documentation</title>
  <link rel="stylesheet" href="../../../../../https@fonts.googleapis.com/css@family=Lato_3A400,700,400italic&display=fallback">
  <link rel="stylesheet" href="assets/style.css">
  <link rel="stylesheet" href="assets/sh.css">
  <link rel="canonical" href="../../../../api/assert.html">
</head>
<body class="alt apidoc" id="api-section-assert">
  <div id="content" class="clearfix">
    <div id="column2" class="interior">
      <div id="intro" class="interior">
        <a href="../../../../default.htm" title="Go back to the home page">
          Node.js
        </a>
      </div>
      <ul>
<li><a href="documentation.html" class="nav-documentation">About these Docs</a></li>
<li><a href="synopsis.html" class="nav-synopsis">Usage &#x26; Example</a></li>
</ul>
<div class="line"></div>
<ul>
<li><a href="assert.html" class="nav-assert active">Assertion Testing</a></li>
<li><a href="async_hooks.html" class="nav-async_hooks">Async Hooks</a></li>
<li><a href="buffer.html" class="nav-buffer">Buffer</a></li>
<li><a href="addons.html" class="nav-addons">C++ Addons</a></li>
<li><a href="n-api.html" class="nav-n-api">C/C++ Addons with N-API</a></li>
<li><a href="child_process.html" class="nav-child_process">Child Processes</a></li>
<li><a href="cluster.html" class="nav-cluster">Cluster</a></li>
<li><a href="cli.html" class="nav-cli">Command Line Options</a></li>
<li><a href="console.html" class="nav-console">Console</a></li>
<li><a href="crypto.html" class="nav-crypto">Crypto</a></li>
<li><a href="debugger.html" class="nav-debugger">Debugger</a></li>
<li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li>
<li><a href="dns.html" class="nav-dns">DNS</a></li>
<li><a href="domain.html" class="nav-domain">Domain</a></li>
<li><a href="esm.html" class="nav-esm">ECMAScript Modules</a></li>
<li><a href="errors.html" class="nav-errors">Errors</a></li>
<li><a href="events.html" class="nav-events">Events</a></li>
<li><a href="fs.html" class="nav-fs">File System</a></li>
<li><a href="globals.html" class="nav-globals">Globals</a></li>
<li><a href="http.html" class="nav-http">HTTP</a></li>
<li><a href="http2.html" class="nav-http2">HTTP/2</a></li>
<li><a href="https.html" class="nav-https">HTTPS</a></li>
<li><a href="inspector.html" class="nav-inspector">Inspector</a></li>
<li><a href="intl.html" class="nav-intl">Internationalization</a></li>
<li><a href="modules.html" class="nav-modules">Modules</a></li>
<li><a href="net.html" class="nav-net">Net</a></li>
<li><a href="os.html" class="nav-os">OS</a></li>
<li><a href="path.html" class="nav-path">Path</a></li>
<li><a href="perf_hooks.html" class="nav-perf_hooks">Performance Hooks</a></li>
<li><a href="policy.html" class="nav-policy">Policies</a></li>
<li><a href="process.html" class="nav-process">Process</a></li>
<li><a href="punycode.html" class="nav-punycode">Punycode</a></li>
<li><a href="querystring.html" class="nav-querystring">Query Strings</a></li>
<li><a href="readline.html" class="nav-readline">Readline</a></li>
<li><a href="repl.html" class="nav-repl">REPL</a></li>
<li><a href="report.html" class="nav-report">Report</a></li>
<li><a href="stream.html" class="nav-stream">Stream</a></li>
<li><a href="string_decoder.html" class="nav-string_decoder">String Decoder</a></li>
<li><a href="timers.html" class="nav-timers">Timers</a></li>
<li><a href="tls.html" class="nav-tls">TLS/SSL</a></li>
<li><a href="tracing.html" class="nav-tracing">Trace Events</a></li>
<li><a href="tty.html" class="nav-tty">TTY</a></li>
<li><a href="dgram.html" class="nav-dgram">UDP/Datagram</a></li>
<li><a href="url.html" class="nav-url">URL</a></li>
<li><a href="util.html" class="nav-util">Utilities</a></li>
<li><a href="v8.html" class="nav-v8">V8</a></li>
<li><a href="vm.html" class="nav-vm">VM</a></li>
<li><a href="wasi.html" class="nav-wasi">WASI</a></li>
<li><a href="worker_threads.html" class="nav-worker_threads">Worker Threads</a></li>
<li><a href="zlib.html" class="nav-zlib">Zlib</a></li>
</ul>
<div class="line"></div>
<ul>
<li><a href="../../../../../https@github.com/nodejs/node" class="nav-https-github-com-nodejs-node">GitHub Repo &#x26; Issue Tracker</a></li>
</ul>
    </div>

    <div id="column1" data-id="assert" class="interior">
      <header>
        <h1>Node.js v12.16.1 Documentation</h1>
        <div id="gtoc">
          <ul>
            <li>
              <a href="index.html" name="toc">Index</a>
            </li>
            <li>
              <a href="all.html">View on single page</a>
            </li>
            <li>
              <a href="assert.json">View as JSON</a>
            </li>
            
    <li class="version-picker">
      <a href="#">View another version <span>&#x25bc;</span></a>
      <ol class="version-picker"><li><a href="../../../../docs/latest-v13.x/api/assert.html">13.x</a></li>
<li><a href="../../../../docs/latest-v12.x/api/assert.html">12.x <b>LTS</b></a></li>
<li><a href="../../../../docs/latest-v11.x/api/assert.html">11.x</a></li>
<li><a href="../../../../docs/latest-v10.x/api/assert.html">10.x <b>LTS</b></a></li>
<li><a href="../../../../docs/latest-v9.x/api/assert.html">9.x</a></li>
<li><a href="../../../../docs/latest-v8.x/api/assert.html">8.x</a></li>
<li><a href="../../../../docs/latest-v7.x/api/assert.html">7.x</a></li>
<li><a href="../../../../docs/latest-v6.x/api/assert.html">6.x</a></li>
<li><a href="../../../../docs/latest-v5.x/api/assert.html">5.x</a></li>
<li><a href="../../../../docs/latest-v4.x/api/assert.html">4.x</a></li>
<li><a href="../../../../docs/latest-v0.12.x/api/assert.html">0.12.x</a></li>
<li><a href="../../../../docs/latest-v0.10.x/api/assert.html">0.10.x</a></li></ol>
    </li>
  
            <li class="edit_on_github"><a href="../../../../../https@github.com/nodejs/node/edit/master/doc/api/assert.md"><span class="github_icon"><svg height="16" width="16" viewBox="0 0 16.1 16.1" fill="currentColor"><path d="M8 0a8 8 0 0 0-2.5 15.6c.4 0 .5-.2.5-.4v-1.5c-2 .4-2.5-.5-2.7-1 0-.1-.5-.9-.8-1-.3-.2-.7-.6 0-.6.6 0 1 .6 1.2.8.7 1.2 1.9 1 2.4.7 0-.5.2-.9.5-1-1.8-.3-3.7-1-3.7-4 0-.9.3-1.6.8-2.2 0-.2-.3-1 .1-2 0 0 .7-.3 2.2.7a7.4 7.4 0 0 1 4 0c1.5-1 2.2-.8 2.2-.8.5 1.1.2 2 .1 2.1.5.6.8 1.3.8 2.2 0 3-1.9 3.7-3.6 4 .3.2.5.7.5 1.4v2.2c0 .2.1.5.5.4A8 8 0 0 0 16 8a8 8 0 0 0-8-8z"/></svg></span>Edit on GitHub</a></li>
          </ul>
        </div>
        <hr>
      </header>

      <div id="toc">
        <h2>Table of Contents</h2>
        <ul>
<li>
<p><span class="stability_2"><a href="#assert_assert">Assert</a></span></p>
<ul>
<li>
<p><a href="#assert_class_assert_assertionerror">Class: assert.AssertionError</a></p>
<ul>
<li><a href="#assert_new_assert_assertionerror_options"><code>new assert.AssertionError(options)</code></a></li>
</ul>
</li>
<li><a href="#assert_strict_mode">Strict mode</a></li>
<li><a href="#assert_legacy_mode">Legacy mode</a></li>
<li><a href="#assert_assert_value_message"><code>assert(value[, message])</code></a></li>
<li>
<p><a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual(actual, expected[, message])</code></a></p>
<ul>
<li><a href="#assert_comparison_details">Comparison details</a></li>
</ul>
</li>
<li>
<p><a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual(actual, expected[, message])</code></a></p>
<ul>
<li><a href="#assert_comparison_details_1">Comparison details</a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#assert_assert_doesnotmatch_string_regexp_message"><code>assert.doesNotMatch(string, regexp[, message])</code></a></span></li>
<li><a href="#assert_assert_doesnotreject_asyncfn_error_message"><code>assert.doesNotReject(asyncFn[, error][, message])</code></a></li>
<li><a href="#assert_assert_doesnotthrow_fn_error_message"><code>assert.doesNotThrow(fn[, error][, message])</code></a></li>
<li><a href="#assert_assert_equal_actual_expected_message"><code>assert.equal(actual, expected[, message])</code></a></li>
<li><a href="#assert_assert_fail_message"><code>assert.fail([message])</code></a></li>
<li><span class="stability_0"><a href="#assert_assert_fail_actual_expected_message_operator_stackstartfn"><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code></a></span></li>
<li><a href="#assert_assert_iferror_value"><code>assert.ifError(value)</code></a></li>
<li><span class="stability_1"><a href="#assert_assert_match_string_regexp_message"><code>assert.match(string, regexp[, message])</code></a></span></li>
<li><a href="#assert_assert_notdeepequal_actual_expected_message"><code>assert.notDeepEqual(actual, expected[, message])</code></a></li>
<li><a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assert_assert_notequal_actual_expected_message"><code>assert.notEqual(actual, expected[, message])</code></a></li>
<li><a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assert_assert_ok_value_message"><code>assert.ok(value[, message])</code></a></li>
<li><a href="#assert_assert_rejects_asyncfn_error_message"><code>assert.rejects(asyncFn[, error][, message])</code></a></li>
<li><a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assert_assert_throws_fn_error_message"><code>assert.throws(fn[, error][, message])</code></a></li>
</ul>
</li>
</ul>
      </div>

      <div id="apicontent">
        <h1>Assert<span><a class="mark" href="#assert_assert" id="assert_assert">#</a></span></h1>

<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p>
<p>The <code>assert</code> module provides a set of assertion functions for verifying
invariants. The module provides a recommended <a href="#assert_strict_mode"><code>strict</code> mode</a> and a more
lenient legacy mode.</p>
<h2>Class: assert.AssertionError<a class="srclink" href="../../../../../https@github.com/nodejs/node/blob/5263cc40be3ad3a0b27605e77996daa6f49bb31a/lib/assert.js#L146">[src]</a><span><a class="mark" href="#assert_class_assert_assertionerror" id="assert_class_assert_assertionerror">#</a></span></h2>
<ul>
<li>Extends: <a href="errors.html#errors_class_error" class="type">&#x3C;errors.Error></a></li>
</ul>
<p>Indicates the failure of an assertion. All errors thrown by the <code>assert</code> module
will be instances of the <code>AssertionError</code> class.</p>
<h3><code>new assert.AssertionError(options)</code><span><a class="mark" href="#assert_new_assert_assertionerror_options" id="assert_new_assert_assertionerror_options">#</a></span></h3>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div>
<ul>
<li>
<p><code>options</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a></p>
<ul>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If provided, the error message is set to this value.</li>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The <code>actual</code> property on the error instance.</li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The <code>expected</code> property on the error instance.</li>
<li><code>operator</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The <code>operator</code> property on the error instance.</li>
<li><code>stackStartFn</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> If provided, the generated stack trace omits
frames before this function.</li>
</ul>
</li>
</ul>
<p>A subclass of <code>Error</code> that indicates the failure of an assertion.</p>
<p>All instances contain the built-in <code>Error</code> properties (<code>message</code> and <code>name</code>)
and:</p>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> Set to the <code>actual</code> argument for methods such as
<a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> Set to the <code>expected</code> value for methods such as
<a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</li>
<li><code>generatedMessage</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Indicates if the message was auto-generated
(<code>true</code>) or not.</li>
<li><code>code</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Value is always <code>ERR_ASSERTION</code> to show that the error is an
assertion error.</li>
<li><code>operator</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Set to the passed in operator value.</li>
</ul>
<pre><code class="language-js">const assert = require('assert');

// Generate an AssertionError to compare the error message later:
const { message } = new assert.AssertionError({
  actual: 1,
  expected: 2,
  operator: 'strictEqual'
});

// Verify error output:
try {
  assert.strictEqual(1, 2);
} catch (err) {
  assert(err instanceof assert.AssertionError);
  assert.strictEqual(err.message, message);
  assert.strictEqual(err.name, 'AssertionError');
  assert.strictEqual(err.actual, 1);
  assert.strictEqual(err.expected, 2);
  assert.strictEqual(err.code, 'ERR_ASSERTION');
  assert.strictEqual(err.operator, 'strictEqual');
  assert.strictEqual(err.generatedMessage, true);
}
</code></pre>
<h2>Strict mode<span><a class="mark" href="#assert_strict_mode" id="assert_strict_mode">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v9.9.0</td>
<td><p>Added error diffs to the strict mode</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>Added strict mode to the assert module.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p><span>Added in: v9.9.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>In <code>strict</code> mode (not to be confused with <code>"use strict"</code>), <code>assert</code> functions
use the comparison in the corresponding strict functions. For example,
<a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> will behave like <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p>
<p>In <code>strict</code> mode, error messages for objects display a diff. In legacy mode,
error messages for objects display the objects, often truncated.</p>
<p>To use <code>strict</code> mode:</p>
<pre><code class="language-js">const assert = require('assert').strict;
</code></pre>
<p>Example error diff:</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected ... Lines skipped
//
//   [
//     [
// ...
//       2,
// +     3
// -     '3'
//     ],
// ...
//     5
//   ]
</code></pre>
<p>To deactivate the colors, use the <code>NO_COLOR</code> or
<code>NODE_DISABLE_COLORS</code> environment variable.
This will also deactivate the colors in the REPL.</p>
<p>For more on the color support in terminal environments, read
the tty <a href="tty.html#tty_writestream_getcolordepth_env">getColorDepth()</a> doc.</p>
<h2>Legacy mode<span><a class="mark" href="#assert_legacy_mode" id="assert_legacy_mode">#</a></span></h2>
<p>Legacy mode uses the <a href="../../../../../https@tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> in:</p>
<ul>
<li><a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a></li>
<li><a href="#assert_assert_equal_actual_expected_message"><code>assert.equal()</code></a></li>
<li><a href="#assert_assert_notdeepequal_actual_expected_message"><code>assert.notDeepEqual()</code></a></li>
<li><a href="#assert_assert_notequal_actual_expected_message"><code>assert.notEqual()</code></a></li>
</ul>
<p>To use legacy mode:</p>
<pre><code class="language-js">const assert = require('assert');
</code></pre>
<p>Whenever possible, use the <a href="#assert_strict_mode"><code>strict</code> mode</a> instead. Otherwise, the
<a href="../../../../../https@tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> may cause surprising results. This is
especially true for <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>, where the comparison rules are
lax:</p>
<pre><code class="language-js">// WARNING: This does not throw an AssertionError!
assert.deepEqual(/a/gi, new Date());
</code></pre>
<h2><code>assert(value[, message])</code><span><a class="mark" href="#assert_assert_value_message" id="assert_assert_value_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div>
<ul>
<li><code>value</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The input that is checked for being truthy.</li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p>An alias of <a href="#assert_assert_ok_value_message"><code>assert.ok()</code></a>.</p>
<h2><code>assert.deepEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_deepequal_actual_expected_message" id="assert_assert_deepequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v12.0.0</td>
<td><p>The type tags are now properly compared and there are a couple minor comparison adjustments to make the check less surprising.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v6.1.0, v4.5.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p><strong>Strict mode</strong></p>
<p>An alias of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p>
<p><strong>Legacy mode</strong></p>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a> instead.</div><p></p>
<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters. Consider
using <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a> instead. <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a> can have
potentially surprising results.</p>
<p>"Deep" equality means that the enumerable "own" properties of child objects
are also recursively evaluated by the following rules.</p>
<h3>Comparison details<span><a class="mark" href="#assert_comparison_details" id="assert_comparison_details">#</a></span></h3>
<ul>
<li>Primitive values are compared with the <a href="../../../../../https@tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a>
( <code>==</code> ).</li>
<li><a href="../../../../../https@tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li>
<li>Only <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li>
<li><a href="errors.html#errors_class_error"><code>Error</code></a> names and messages are always compared, even if these are not
enumerable properties.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li>
<li><code>Object</code> properties are compared unordered.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> keys and <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> items are compared unordered.</li>
<li>Recursion stops when both sides differ or both sides encounter a circular
reference.</li>
<li>Implementation does not test the <a href="../../../../../https@tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of
objects.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are not compared.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values.</li>
</ul>
<p>The following example does not throw an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> because the
primitives are considered equal by the <a href="../../../../../https@tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a>
( <code>==</code> ).</p>
<pre><code class="language-js">// WARNING: This does not throw an AssertionError!
assert.deepEqual('+00000000', false);
</code></pre>
<p>"Deep" equality means that the enumerable "own" properties of child objects
are evaluated also:</p>
<pre><code class="language-js">const assert = require('assert');

const obj1 = {
  a: {
    b: 1
  }
};
const obj2 = {
  a: {
    b: 2
  }
};
const obj3 = {
  a: {
    b: 1
  }
};
const obj4 = Object.create(obj1);

assert.deepEqual(obj1, obj1);
// OK

// Values of b are different:
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }

assert.deepEqual(obj1, obj3);
// OK

// Prototypes are ignored:
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
</code></pre>
<p>If the values are not equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<h2><code>assert.deepStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_deepstrictequal_actual_expected_message" id="assert_assert_deepstrictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v9.0.0</td>
<td><p>Enumerable symbol properties are now compared.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>NaN</code> is now compared using the <a href="../../../../../https@tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p></td></tr>
<tr><td>v8.5.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v1.2.0</td>
<td><p><span>Added in: v1.2.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters.
"Deep" equality means that the enumerable "own" properties of child objects
are recursively evaluated also by the following rules.</p>
<h3>Comparison details<span><a class="mark" href="#assert_comparison_details_1" id="assert_comparison_details_1">#</a></span></h3>
<ul>
<li>Primitive values are compared using the <a href="../../../../../https@tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>, used by
<a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is"><code>Object.is()</code></a>.</li>
<li><a href="../../../../../https@tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li>
<li><a href="../../../../../https@tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of objects are compared using
the <a href="../../../../../https@tc39.github.io/ecma262/#sec-strict-equality-comparison">Strict Equality Comparison</a>.</li>
<li>Only <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li>
<li><a href="errors.html#errors_class_error"><code>Error</code></a> names and messages are always compared, even if these are not
enumerable properties.</li>
<li>Enumerable own <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are compared as well.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li>
<li><code>Object</code> properties are compared unordered.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> keys and <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> items are compared unordered.</li>
<li>Recursion stops when both sides differ or both sides encounter a circular
reference.</li>
<li><a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values. See
below for further details.</li>
</ul>
<pre><code class="language-js">const assert = require('assert').strict;

// This fails because 1 !== '1'.
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
//   {
// +   a: 1
// -   a: '1'
//   }

// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);

// Different [[Prototype]]:
assert.deepStrictEqual(object, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + {}
// - Date {}

// Different type tags:
assert.deepStrictEqual(date, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 2018-04-26T00:49:08.604Z
// - Date {}

assert.deepStrictEqual(NaN, NaN);
// OK, because of the SameValue comparison

// Different unwrapped numbers:
assert.deepStrictEqual(new Number(1), new Number(2));
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + [Number: 1]
// - [Number: 2]

assert.deepStrictEqual(new String('foo'), Object('foo'));
// OK because the object and the string are identical when unwrapped.

assert.deepStrictEqual(-0, -0);
// OK

// Different zeros using the SameValue Comparison:
assert.deepStrictEqual(0, -0);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 0
// - -0

const symbol1 = Symbol();
const symbol2 = Symbol();
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });
// OK, because it is the same symbol on both objects.

assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:
//
// {
//   [Symbol()]: 1
// }

const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;

assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries

// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
//   WeakMap {
// +   [items unknown]
// -   [items unknown],
// -   unequal: true
//   }
</code></pre>
<p>If the values are not equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.</p>
<h2><code>assert.doesNotMatch(string, regexp[, message])</code><span><a class="mark" href="#assert_assert_doesnotmatch_string_regexp_message" id="assert_assert_doesnotmatch_string_regexp_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v12.16.0</span>
</div>
<ul>
<li><code>string</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a></li>
<li><code>regexp</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p>
<p>Expects the <code>string</code> input not to match the regular expression.</p>
<p>This feature is currently experimental and the name might change or it might be
completely removed again.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.doesNotMatch('I will fail', /fail/);
// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...

assert.doesNotMatch(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.

assert.doesNotMatch('I will pass', /different/);
// OK
</code></pre>
<p>If the values do match, or if the <code>string</code> argument is of another type than
<code>string</code>, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> property set equal
to the value of the <code>message</code> parameter. If the <code>message</code> parameter is
undefined, a default error message is assigned. If the <code>message</code> parameter is an
instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<h2><code>assert.doesNotReject(asyncFn[, error][, message])</code><span><a class="mark" href="#assert_assert_doesnotreject_asyncfn_error_message" id="assert_assert_doesnotreject_asyncfn_error_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>asyncFn</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a></li>
<li><code>error</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a></li>
</ul>
<p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately
calls the function and awaits the returned promise to complete. It will then
check that the promise is not rejected.</p>
<p>If <code>asyncFn</code> is a function and it throws an error synchronously,
<code>assert.doesNotReject()</code> will return a rejected <code>Promise</code> with that error. If
the function does not return a promise, <code>assert.doesNotReject()</code> will return a
rejected <code>Promise</code> with an <a href="errors.html#errors_err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases
the error handler is skipped.</p>
<p>Using <code>assert.doesNotReject()</code> is actually not useful because there is little
benefit in catching a rejection and then rejecting it again. Instead, consider
adding a comment next to the specific code path that should not reject and keep
error messages as expressive as possible.</p>
<p>If specified, <code>error</code> can be a <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> or a validation
function. See <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> for more details.</p>
<p>Besides the async nature to await the completion behaves identically to
<a href="#assert_assert_doesnotthrow_fn_error_message"><code>assert.doesNotThrow()</code></a>.</p>
<!-- eslint-disable no-restricted-syntax -->
<pre><code class="language-js">(async () => {
  await assert.doesNotReject(
    async () => {
      throw new TypeError('Wrong value');
    },
    SyntaxError
  );
})();
</code></pre>
<!-- eslint-disable no-restricted-syntax -->
<pre><code class="language-js">assert.doesNotReject(Promise.reject(new TypeError('Wrong value')))
  .then(() => {
    // ...
  });
</code></pre>
<h2><code>assert.doesNotThrow(fn[, error][, message])</code><span><a class="mark" href="#assert_assert_doesnotthrow_fn_error_message" id="assert_assert_doesnotthrow_fn_error_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v5.11.0, v4.4.5</td>
<td><p>The <code>message</code> parameter is respected now.</p></td></tr>
<tr><td>v4.2.0</td>
<td><p>The <code>error</code> parameter can now be an arrow function.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>fn</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a></li>
<li><code>error</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a></li>
</ul>
<p>Asserts that the function <code>fn</code> does not throw an error.</p>
<p>Using <code>assert.doesNotThrow()</code> is actually not useful because there
is no benefit in catching an error and then rethrowing it. Instead, consider
adding a comment next to the specific code path that should not throw and keep
error messages as expressive as possible.</p>
<p>When <code>assert.doesNotThrow()</code> is called, it will immediately call the <code>fn</code>
function.</p>
<p>If an error is thrown and it is the same type as that specified by the <code>error</code>
parameter, then an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown. If the error is of a
different type, or if the <code>error</code> parameter is undefined, the error is
propagated back to the caller.</p>
<p>If specified, <code>error</code> can be a <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> or a validation
function. See <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> for more details.</p>
<p>The following, for instance, will throw the <a href="errors.html#errors_class_typeerror"><code>TypeError</code></a> because there is no
matching error type in the assertion:</p>
<!-- eslint-disable no-restricted-syntax -->
<pre><code class="language-js">assert.doesNotThrow(
  () => {
    throw new TypeError('Wrong value');
  },
  SyntaxError
);
</code></pre>
<p>However, the following will result in an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> with the message
'Got unwanted exception...':</p>
<!-- eslint-disable no-restricted-syntax -->
<pre><code class="language-js">assert.doesNotThrow(
  () => {
    throw new TypeError('Wrong value');
  },
  TypeError
);
</code></pre>
<p>If an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown and a value is provided for the <code>message</code>
parameter, the value of <code>message</code> will be appended to the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>
message:</p>
<!-- eslint-disable no-restricted-syntax -->
<pre><code class="language-js">assert.doesNotThrow(
  () => {
    throw new TypeError('Wrong value');
  },
  /Wrong value/,
  'Whoops'
);
// Throws: AssertionError: Got unwanted exception: Whoops
</code></pre>
<h2><code>assert.equal(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_equal_actual_expected_message" id="assert_assert_equal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p><strong>Strict mode</strong></p>
<p>An alias of <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a>.</p>
<p><strong>Legacy mode</strong></p>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="#assert_assert_strictequal_actual_expected_message"><code>assert.strictEqual()</code></a> instead.</div><p></p>
<p>Tests shallow, coercive equality between the <code>actual</code> and <code>expected</code> parameters
using the <a href="../../../../../https@tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a> ( <code>==</code> ).</p>
<pre><code class="language-js">const assert = require('assert');

assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'

assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
</code></pre>
<p>If the values are not equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.</p>
<h2><code>assert.fail([message])</code><span><a class="mark" href="#assert_assert_fail_message" id="assert_assert_fail_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div>
<ul>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> <strong>Default:</strong> <code>'Failed'</code></li>
</ul>
<p>Throws an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> with the provided error message or a default
error message. If the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then
it will be thrown instead of the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.fail();
// AssertionError [ERR_ASSERTION]: Failed

assert.fail('boom');
// AssertionError [ERR_ASSERTION]: boom

assert.fail(new TypeError('need array'));
// TypeError: need array
</code></pre>
<p>Using <code>assert.fail()</code> with more than two arguments is possible but deprecated.
See below for further details.</p>
<h2><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code><span><a class="mark" href="#assert_assert_fail_actual_expected_message_operator_stackstartfn" id="assert_assert_fail_actual_expected_message_operator_stackstartfn">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Calling <code>assert.fail()</code> with more than one argument is deprecated and emits a warning.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>assert.fail([message])</code> or other assert
functions instead.</div><p></p>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
<li><code>operator</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> <strong>Default:</strong> <code>'!='</code></li>
<li><code>stackStartFn</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> <strong>Default:</strong> <code>assert.fail</code></li>
</ul>
<p>If <code>message</code> is falsy, the error message is set as the values of <code>actual</code> and
<code>expected</code> separated by the provided <code>operator</code>. If just the two <code>actual</code> and
<code>expected</code> arguments are provided, <code>operator</code> will default to <code>'!='</code>. If
<code>message</code> is provided as third argument it will be used as the error message and
the other arguments will be stored as properties on the thrown object. If
<code>stackStartFn</code> is provided, all stack frames above that function will be
removed from stacktrace (see <a href="errors.html#errors_error_capturestacktrace_targetobject_constructoropt"><code>Error.captureStackTrace</code></a>). If no arguments are
given, the default message <code>Failed</code> will be used.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.fail('a', 'b');
// AssertionError [ERR_ASSERTION]: 'a' != 'b'

assert.fail(1, 2, undefined, '>');
// AssertionError [ERR_ASSERTION]: 1 > 2

assert.fail(1, 2, 'fail');
// AssertionError [ERR_ASSERTION]: fail

assert.fail(1, 2, 'whoops', '>');
// AssertionError [ERR_ASSERTION]: whoops

assert.fail(1, 2, new TypeError('need array'));
// TypeError: need array
</code></pre>
<p>In the last three cases <code>actual</code>, <code>expected</code>, and <code>operator</code> have no
influence on the error message.</p>
<p>Example use of <code>stackStartFn</code> for truncating the exception's stacktrace:</p>
<pre><code class="language-js">function suppressFrame() {
  assert.fail('a', 'b', undefined, '!==', suppressFrame);
}
suppressFrame();
// AssertionError [ERR_ASSERTION]: 'a' !== 'b'
//     at repl:1:1
//     at ContextifyScript.Script.runInThisContext (vm.js:44:33)
//     ...
</code></pre>
<h2><code>assert.ifError(value)</code><span><a class="mark" href="#assert_assert_iferror_value" id="assert_assert_iferror_value">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Instead of throwing the original error it is now wrapped into an [<code>AssertionError</code>][] that contains the full stack trace.</p></td></tr>
<tr><td>v10.0.0</td>
<td><p>Value may now only be <code>undefined</code> or <code>null</code>. Before all falsy values were handled the same as <code>null</code> and did not throw.</p></td></tr>
<tr><td>v0.1.97</td>
<td><p><span>Added in: v0.1.97</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>value</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
</ul>
<p>Throws <code>value</code> if <code>value</code> is not <code>undefined</code> or <code>null</code>. This is useful when
testing the <code>error</code> argument in callbacks. The stack trace contains all frames
from the error passed to <code>ifError()</code> including the potential new frames for
<code>ifError()</code> itself.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.ifError(null);
// OK
assert.ifError(0);
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0
assert.ifError('error');
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'
assert.ifError(new Error());
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error

// Create some random error frames.
let err;
(function errorFrame() {
  err = new Error('test error');
})();

(function ifErrorFrame() {
  assert.ifError(err);
})();
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error
//     at ifErrorFrame
//     at errorFrame
</code></pre>
<h2><code>assert.match(string, regexp[, message])</code><span><a class="mark" href="#assert_assert_match_string_regexp_message" id="assert_assert_match_string_regexp_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v12.16.0</span>
</div>
<ul>
<li><code>string</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a></li>
<li><code>regexp</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p>
<p>Expects the <code>string</code> input to match the regular expression.</p>
<p>This feature is currently experimental and the name might change or it might be
completely removed again.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.match('I will fail', /pass/);
// AssertionError [ERR_ASSERTION]: The input did not match the regular ...

assert.match(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.

assert.match('I will pass', /pass/);
// OK
</code></pre>
<p>If the values do not match, or if the <code>string</code> argument is of another type than
<code>string</code>, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> property set equal
to the value of the <code>message</code> parameter. If the <code>message</code> parameter is
undefined, a default error message is assigned. If the <code>message</code> parameter is an
instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<h2><code>assert.notDeepEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notdeepequal_actual_expected_message" id="assert_assert_notdeepequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v6.1.0, v4.5.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p><strong>Strict mode</strong></p>
<p>An alias of <a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual()</code></a>.</p>
<p><strong>Legacy mode</strong></p>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="#assert_assert_notdeepstrictequal_actual_expected_message"><code>assert.notDeepStrictEqual()</code></a> instead.</div><p></p>
<p>Tests for any deep inequality. Opposite of <a href="#assert_assert_deepequal_actual_expected_message"><code>assert.deepEqual()</code></a>.</p>
<pre><code class="language-js">const assert = require('assert');

const obj1 = {
  a: {
    b: 1
  }
};
const obj2 = {
  a: {
    b: 2
  }
};
const obj3 = {
  a: {
    b: 1
  }
};
const obj4 = Object.create(obj1);

assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }

assert.notDeepEqual(obj1, obj2);
// OK

assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }

assert.notDeepEqual(obj1, obj4);
// OK
</code></pre>
<p>If the values are deeply equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned. If the
<code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown
instead of the <code>AssertionError</code>.</p>
<h2><code>assert.notDeepStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notdeepstrictequal_actual_expected_message" id="assert_assert_notdeepstrictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>-0</code> and <code>+0</code> are not considered equal anymore.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>NaN</code> is now compared using the <a href="../../../../../https@tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v1.2.0</td>
<td><p><span>Added in: v1.2.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p>Tests for deep strict inequality. Opposite of <a href="#assert_assert_deepstrictequal_actual_expected_message"><code>assert.deepStrictEqual()</code></a>.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
</code></pre>
<p>If the values are deeply and strictly equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown
with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If
the <code>message</code> parameter is undefined, a default error message is assigned. If
the <code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown
instead of the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<h2><code>assert.notEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notequal_actual_expected_message" id="assert_assert_notequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p><strong>Strict mode</strong></p>
<p>An alias of <a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual()</code></a>.</p>
<p><strong>Legacy mode</strong></p>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <a href="#assert_assert_notstrictequal_actual_expected_message"><code>assert.notStrictEqual()</code></a> instead.</div><p></p>
<p>Tests shallow, coercive inequality with the <a href="../../../../../https@tc39.github.io/ecma262/#sec-abstract-equality-comparison">Abstract Equality Comparison</a>
( <code>!=</code> ).</p>
<pre><code class="language-js">const assert = require('assert');

assert.notEqual(1, 2);
// OK

assert.notEqual(1, 1);
// AssertionError: 1 != 1

assert.notEqual(1, '1');
// AssertionError: 1 != '1'
</code></pre>
<p>If the values are equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.</p>
<h2><code>assert.notStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_notstrictequal_actual_expected_message" id="assert_assert_notstrictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Used comparison changed from Strict Equality to <code>Object.is()</code></p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p>Tests strict inequality between the <code>actual</code> and <code>expected</code> parameters as
determined by the <a href="../../../../../https@tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.notStrictEqual(1, 2);
// OK

assert.notStrictEqual(1, 1);
// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:
//
// 1

assert.notStrictEqual(1, '1');
// OK
</code></pre>
<p>If the values are strictly equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned. If the
<code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown
instead of the <code>AssertionError</code>.</p>
<h2><code>assert.ok(value[, message])</code><span><a class="mark" href="#assert_assert_ok_value_message" id="assert_assert_ok_value_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>The <code>assert.ok()</code> (no arguments) will now use a predefined error message.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>value</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p>Tests if <code>value</code> is truthy. It is equivalent to
<code>assert.equal(!!value, true, message)</code>.</p>
<p>If <code>value</code> is not truthy, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is <code>undefined</code>, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.
If no arguments are passed in at all <code>message</code> will be set to the string:
<code>'No value argument passed to `assert.ok()`'</code>.</p>
<p>Be aware that in the <code>repl</code> the error message will be different to the one
thrown in a file! See below for further details.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.ok(true);
// OK
assert.ok(1);
// OK

assert.ok();
// AssertionError: No value argument passed to `assert.ok()`

assert.ok(false, 'it\'s false');
// AssertionError: it's false

// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true

// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(typeof 123 === 'string')

assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(false)

assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert.ok(0)

// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
//   assert(0)
</code></pre>
<h2><code>assert.rejects(asyncFn[, error][, message])</code><span><a class="mark" href="#assert_assert_rejects_asyncfn_error_message" id="assert_assert_rejects_asyncfn_error_message">#</a></span></h2>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>asyncFn</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a></li>
<li><code>error</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a></li>
</ul>
<p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately
calls the function and awaits the returned promise to complete. It will then
check that the promise is rejected.</p>
<p>If <code>asyncFn</code> is a function and it throws an error synchronously,
<code>assert.rejects()</code> will return a rejected <code>Promise</code> with that error. If the
function does not return a promise, <code>assert.rejects()</code> will return a rejected
<code>Promise</code> with an <a href="errors.html#errors_err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases the error
handler is skipped.</p>
<p>Besides the async nature to await the completion behaves identically to
<a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a>.</p>
<p>If specified, <code>error</code> can be a <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function,
an object where each property will be tested for, or an instance of error where
each property will be tested for including the non-enumerable <code>message</code> and
<code>name</code> properties.</p>
<p>If specified, <code>message</code> will be the message provided by the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>
if the <code>asyncFn</code> fails to reject.</p>
<pre><code class="language-js">(async () => {
  await assert.rejects(
    async () => {
      throw new TypeError('Wrong value');
    },
    {
      name: 'TypeError',
      message: 'Wrong value'
    }
  );
})();
</code></pre>
<pre><code class="language-js">assert.rejects(
  Promise.reject(new Error('Wrong value')),
  Error
).then(() => {
  // ...
});
</code></pre>
<p><code>error</code> cannot be a string. If a string is provided as the second
argument, then <code>error</code> is assumed to be omitted and the string will be used for
<code>message</code> instead. This can lead to easy-to-miss mistakes. Please read the
example in <a href="#assert_assert_throws_fn_error_message"><code>assert.throws()</code></a> carefully if using a string as the second
argument gets considered.</p>
<h2><code>assert.strictEqual(actual, expected[, message])</code><span><a class="mark" href="#assert_assert_strictequal_actual_expected_message" id="assert_assert_strictequal_actual_expected_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Used comparison changed from Strict Equality to <code>Object.is()</code></p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>expected</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
</ul>
<p>Tests strict equality between the <code>actual</code> and <code>expected</code> parameters as
determined by the <a href="../../../../../https@tc39.github.io/ecma262/#sec-samevalue">SameValue Comparison</a>.</p>
<pre><code class="language-js">const assert = require('assert').strict;

assert.strictEqual(1, 2);
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
//
// 1 !== 2

assert.strictEqual(1, 1);
// OK

assert.strictEqual('Hello foobar', 'Hello World!');
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
// + actual - expected
//
// + 'Hello foobar'
// - 'Hello World!'
//          ^

const apples = 1;
const oranges = 2;
assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);
// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2

assert.strictEqual(1, '1', new TypeError('Inputs are not identical'));
// TypeError: Inputs are not identical
</code></pre>
<p>If the values are not strictly equal, an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned. If the
<code>message</code> parameter is an instance of an <a href="errors.html#errors_class_error"><code>Error</code></a> then it will be thrown
instead of the <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<h2><code>assert.throws(fn[, error][, message])</code><span><a class="mark" href="#assert_assert_throws_fn_error_message" id="assert_assert_throws_fn_error_message">#</a></span></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.2.0</td>
<td><p>The <code>error</code> parameter can be an object containing regular expressions now.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>The <code>error</code> parameter can now be an object as well.</p></td></tr>
<tr><td>v4.2.0</td>
<td><p>The <code>error</code> parameter can now be an arrow function.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>fn</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a></li>
<li><code>error</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type">&#x3C;RegExp></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> | <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a></li>
<li><code>message</code> <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a></li>
</ul>
<p>Expects the function <code>fn</code> to throw an error.</p>
<p>If specified, <code>error</code> can be a <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function,
a validation object where each property will be tested for strict deep equality,
or an instance of error where each property will be tested for strict deep
equality including the non-enumerable <code>message</code> and <code>name</code> properties. When
using an object, it is also possible to use a regular expression, when
validating against a string property. See below for examples.</p>
<p>If specified, <code>message</code> will be appended to the message provided by the
<code>AssertionError</code> if the <code>fn</code> call fails to throw or in case the error validation
fails.</p>
<p>Custom validation object/error instance:</p>
<pre><code class="language-js">const err = new TypeError('Wrong value');
err.code = 404;
err.foo = 'bar';
err.info = {
  nested: true,
  baz: 'text'
};
err.reg = /abc/i;

assert.throws(
  () => {
    throw err;
  },
  {
    name: 'TypeError',
    message: 'Wrong value',
    info: {
      nested: true,
      baz: 'text'
    }
    // Only properties on the validation object will be tested for.
    // Using nested objects requires all properties to be present. Otherwise
    // the validation is going to fail.
  }
);

// Using regular expressions to validate error properties:
assert.throws(
  () => {
    throw err;
  },
  {
    // The `name` and `message` properties are strings and using regular
    // expressions on those will match against the string. If they fail, an
    // error is thrown.
    name: /^TypeError$/,
    message: /Wrong/,
    foo: 'bar',
    info: {
      nested: true,
      // It is not possible to use regular expressions for nested properties!
      baz: 'text'
    },
    // The `reg` property contains a regular expression and only if the
    // validation object contains an identical regular expression, it is going
    // to pass.
    reg: /abc/i
  }
);

// Fails due to the different `message` and `name` properties:
assert.throws(
  () => {
    const otherErr = new Error('Not found');
    // Copy all enumerable properties from `err` to `otherErr`.
    for (const [key, value] of Object.entries(err)) {
      otherErr[key] = value;
    }
    throw otherErr;
  },
  // The error's `message` and `name` properties will also be checked when using
  // an error as validation object.
  err
);
</code></pre>
<p>Validate instanceof using constructor:</p>
<pre><code class="language-js">assert.throws(
  () => {
    throw new Error('Wrong value');
  },
  Error
);
</code></pre>
<p>Validate error message using <a href="../../../../../https@developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>:</p>
<p>Using a regular expression runs <code>.toString</code> on the error object, and will
therefore also include the error name.</p>
<pre><code class="language-js">assert.throws(
  () => {
    throw new Error('Wrong value');
  },
  /^Error: Wrong value$/
);
</code></pre>
<p>Custom error validation:</p>
<p>The function must return <code>true</code> to indicate all internal validations passed.
It will otherwise fail with an <a href="#assert_class_assert_assertionerror"><code>AssertionError</code></a>.</p>
<pre><code class="language-js">assert.throws(
  () => {
    throw new Error('Wrong value');
  },
  (err) => {
    assert(err instanceof Error);
    assert(/value/.test(err));
    // Avoid returning anything from validation functions besides `true`.
    // Otherwise, it's not clear what part of the validation failed. Instead,
    // throw an error about the specific validation that failed (as done in this
    // example) and add as much helpful debugging information to that error as
    // possible.
    return true;
  },
  'unexpected error'
);
</code></pre>
<p><code>error</code> cannot be a string. If a string is provided as the second
argument, then <code>error</code> is assumed to be omitted and the string will be used for
<code>message</code> instead. This can lead to easy-to-miss mistakes. Using the same
message as the thrown error message is going to result in an
<code>ERR_AMBIGUOUS_ARGUMENT</code> error. Please read the example below carefully if using
a string as the second argument gets considered:</p>
<!-- eslint-disable no-restricted-syntax -->
<pre><code class="language-js">function throwingFirst() {
  throw new Error('First');
}

function throwingSecond() {
  throw new Error('Second');
}

function notThrowing() {}

// The second argument is a string and the input function threw an Error.
// The first case will not throw as it does not match for the error message
// thrown by the input function!
assert.throws(throwingFirst, 'Second');
// In the next example the message has no benefit over the message from the
// error and since it is not clear if the user intended to actually match
// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.
assert.throws(throwingSecond, 'Second');
// TypeError [ERR_AMBIGUOUS_ARGUMENT]

// The string is only used (as message) in case the function does not throw:
assert.throws(notThrowing, 'Second');
// AssertionError [ERR_ASSERTION]: Missing expected exception: Second

// If it was intended to match for the error message do this instead:
// It does not throw because the error messages match.
assert.throws(throwingSecond, /Second$/);

// If the error message does not match, an AssertionError is thrown.
assert.throws(throwingFirst, /Second$/);
// AssertionError [ERR_ASSERTION]
</code></pre>
<p>Due to the confusing error-prone notation, avoid a string as the second
argument.</p>
      </div>
    </div>
  </div>
  <script src="assets/sh_main.js"></script>
  <script src="assets/sh_javascript.min.js"></script>
  <script>highlight(undefined, undefined, 'pre');</script>
</body>
</html>
